CELL DIVISION IN EGGS OF CREPIDULA. 587 



Fig. 112. Exp. 1016: Eggs placed for 27 hrs. in sea water which had been boiled and cooled; similar 

 to Dreceding, development stopped. 



Fig 113. Exp. 1017: Eggs left for 48 hrs. in stoppered test tube of boiled and cooled sea water; 

 development completely stopped; sphere granules prominent. 



Fig 114. Exp. 1016: Same as fig. 112; nuclei with little chromatin; sphere granules prominent. 



Fig! 115.' Exp. 1023: Eggs subjected to atmosphere of hydrogen for 2 hrs. and then left in oj>en bottle 

 for 2 hrs.' development stopped; eggs similar to all others subjected to decreased oxygen tension. 



Fig. 116. Exp. 1017: Same as in fig. 113: The spindles are small, deep-staining and without astral 

 ravs ' the chromosomes are arranged in a ring around the spindles. 



Figs. 1 17-1 18. Exp. 1025 : Eggs left for 18 hrs. in stoppered bottle of sea water through which hydrogen 

 had been run for 1 hr.; eggs similar to fig. 115; in fig. 118 there is an area of yolk (Y) around the upper 

 poles of the spindles. 



PLATE LU. 



Effects of Carbonic Acid. 



Eggs in 1-8-cell stage left for 28 hrs. in sea water J saturated with CO*. 



Fig. 119. Exp. 1163: Egg showing the individually distinct chromosomal vesicles of the maturation 



dons; also 

 Fig. 120. 

 gmented j 



Fig. 121. 

 Fig. 122. 



asmic cells (one of them wi 



an egg similar 



Exp. 1163: The second polar body is abnormally large; an accessory aster (S) lies in the yolk ; 

 t.. c u.»i«w. v» the nucleus in the 1st cleavage has taken place normally, though the spheres are prevented 

 from moving to their normal positions above the nuclei by the presence of the large polar body; the cleavage 

 furrow cuts into the egg from the animal pole side only, and ends in a " cleavage head" as in coelenterrt e eggs. 

 Fig. 123. Exp. 1163: The C and D quadrants are entirely normal; in the blastomere AB, the nucleus 

 divided but the cell did not; these two nuclei in an undivided cell gave off a single blastomere of th( first 

 set (lab) with large lobulated nucleus, the nuclei, spheres and cytoplasmic areas of the cell AB then came 

 to lie at opposite sides of the macromere and each divided independently giving rise to a second micromere 



(2a, 26) which is nearly normal. t . 



Fig. 124. Exp. 1163: There are three macromeres one of which contains a perfect spindle but no 

 chromatin; another contains a polyaster and has given off a large micromere with three nuclei; the third 

 contains a single nucleus which is smaller than normal and has given off in reversed cleavage a 1st and a 2d 



micromere, the former of which is dividing. ....... . . , OJ 



Fig. 125. Exp. 1163: The first cleavage furrow failed to appear though the nuclei divided; atrthe 2d 



with its adiacent ooplasm 



micromere 



Fig. 126. Exp. 1163: Three macromeres one of which contains several centrosomes and spheres 

 Dut no nucleus; another contains a bifurcated spindle and a normal one and has just given off two micro- 

 ns nnfi nn the riaht. n.nd one on the left: the other macromere contains a single nucleus and sphere and has 



micromere 

 Fig. 127. 



micromere on the right; two large micromeres with 

 teld. There is a general resemblance of this egg to ' 

 TCxn. 1163: Side view of ester with two macromeres 



Strands of 



run from the Dolar bodies to the micromeres 



gesting the "spinning" activities of other eggs; lobes are also tound on several ceiis. . 



Fig. 128. Exp. 1163: Two macromeres, each with two nuclei and two or more spheres; in the second 

 cleavage the nuclei divided but the cell-body did not; in the third cleavage there was probably a tnast.er 

 in each macromere, since only two micromeres of the first set were formed (lab, led) each with multiple 

 nuclei; in the fourth cleavage each macromere contained two separate spindles and gave oft two separate 

 micromeres (2a. 26. 2c. 2d) of the second set: the nuclei in the macromeres are so well separated that it is 



spindles would form 



micromeres 



Fig. 129. Exp. 1163: Macromeres A and B did not separate at the 2d cleavage out eacn nas given 

 rise to three micromeres forming a typical micromere plate, though the direction of division m A and js 



has sometimes been atypical. ,., . ., ... ,,_ 



Fig. 130. Exp. 1164: Irregular cleavage mass in which it is not possible to identify many ceils. 



Several of the cells show loose membranes and lobes. , , , . 



Fig. 131. Exp. 1163: One of the macromeres (D) was separated from the other three, but eacn nas 

 given rise to three micromeres which have subdivided in normal manner, the micromeres formed trom u 

 lying on the right of the micromere plate formed from the other macromeres. 



PLATE LIII. 



Effects of Diluted Sea Water 



140, 144 the dilution was one part sea wah 

 was diluted with 



dilutions the blasto- 



meres tend to separate but do not swell appreciably. 



